Anticipated results. Successful completion of the primary analysis of Specific Aim 1 would identify that individuals in the top quintile of QT genotype score demonstrate greater QT prolongation in response to exposure to moxifloxacin than those in the bottom quintile. This would have important implications for the use of genetic predictors in understanding and management of drug-induced QT prolongation. For one, it would demonstrate in principle that a simple genetic test is predictive of risk of drug-induced QT prolongation. Such an analysis could be performed on patients prior to the use of currently approved QT-prolonging medications. Second, it would demonstrate that genes associated with QT prolongation at baseline are also associated with risk of drug-induced QT prolongation. This finding would have implications at both a risk-predictive level, as above, but also in our physiological understanding of the mechanisms of drug-induced QT prolongation.